Higher Wavenumbers Research Articles

P-type semiconductor Gd/Fe ion doped Ni-Mg nanoferrites applications

Citrate gel-auto combustion was used to create gadolinium doped Ni-Mg ferrites with the chemical formula Ni0.8Mg0.2GdxFe2-xO4 (NMGF) with compositions x = (0.00, 0.005, 0.010, 0.015, 0.020, and 0.025). Gadolinium substitution has been studied to see how it affects the structural and electrical characteristics of Ni-Mg complexes. The NMGF crystallizes into a cubic spinel structure, with no secondary phase emerging, according to X-ray diffraction patterns. The elemental composition analysis validates the existence of the predicted components in the samples based on stoichiometry. Images taken with a transmission electron microscope with high resolution and a scanning electron microscope indicate the type of grain formation as well as the particle size of the produced materials. As compared to undoped Ni-Mg ferrite, Fourier transform infrared spectroscopy verifies the establishment of spinel phase and predicts the movement of bands corresponding to Fe-O vibrations towards higher wavenumbers. The samples were measured for conductivity at temperatures ranging from 300 to 723 K. Conductivity measurements revealed the ferromagnetic to paramagnetic transition temperature (Tc) for all materials. The activation energy was determined below and above Tc. TEP measurements of NMGF ferrites were made using a differential technique at temperatures ranging from 300 to 723 K. The prepared ferrites' Seebeck coefficient (S) rose with increasing temperature.

Oblique-mode breakdown of the vertical buoyancy layer

The O-type transition caused by a pair of small-amplitude oblique waves in a vertical buoyancy layer of a fluid with Prandtl number $0.71$ at a Reynolds number of $200$ is investigated using linear stability analysis and three-dimensional direct numerical simulation. The small-amplitude oblique waves experience linear growth and undergo nonlinear interactions to generate streamwise vortices/streaks, two-dimensional streamwise waves and harmonic oblique waves. The streamwise vortices/streaks and two-dimensional streamwise waves have twice the spanwise or streamwise wavenumber of the original perturbation, respectively. Unlike the O-type transition in isothermal flat-plate incompressible and compressible boundary layers where streaks dominate the transition, in the vertical buoyancy layer, either streaks or two-dimensional streamwise waves can dominate the flow field during the early stages of oblique transition. The growth rates of streaks and two-dimensional waves are dependent on the wavenumber of the initial oblique waves. Streaks dominate the flow for high streamwise wavenumbers, while two-dimensional streamwise waves dominate the flow for low streamwise wavenumbers. Analysis of the turbulent kinetic energy production and the Reynolds stresses reveals that the early stages of the transition differ depending on the wavenumber of the oblique waves. An increase in the initial amplitude of the oblique waves causes a faster transition from laminar flow; however, the growth rates of the streaks and two-dimensional streamwise waves are independent of the initial amplitude. Even though different modes are dominant during the early stages of the O-type transition, the onset of chaotic flow is caused by the breakdown of streak modes.

Investigation of effects on turbulent heat transfer of twisted wavy tape elements in the tube

In this study, the turbulence effects created by the twisted wavy tape elements placed inside a plain tube were investigated with experimental results. Changes in heat transfer and pressure drop due to turbulence generation by the tape elements were examined experimentally. The results obtained for a plain tube were compared to the literature and the experimental system was validated. The Re range of the experiments was between 5000 and 20,000. Geometrical parameters were two different amplitudes of twisted wavy tape elements with a single width value and a single twist ratio. In addition, by changing the number of waves, a total of 6 twisted wavy tape elements were used. According to the results, the highest performance factor is obtained around Re = 5000 for the lowest twisted wavy tape element amplitude and highest wavenumber. On the other hand, the minimum pressure drop is calculated for the minimum wavenumber. In addition, it is observed that there is an increase in pressure drop and heat transfer depending on the increase in the number of waves. Compared to the twisted tape element, a performance enhancement of around 42% was found in the case of the twisted wavy tape element.

Stabilized neural ordinary differential equations for long-time forecasting of dynamical systems

In data-driven modeling of spatiotemporal phenomena careful consideration is needed in capturing the dynamics of the high wavenumbers. This problem becomes especially challenging when the system of interest exhibits shocks or chaotic dynamics. We present a data-driven modeling method that accurately captures shocks and chaotic dynamics by proposing a new architecture, stabilized neural ordinary differential equation (ODE). In our proposed architecture, we learn the right-hand-side (RHS) of an ODE by adding the outputs of two NN together where one learns a linear term and the other a nonlinear term. Specifically, we implement this by training a sparse linear convolutional NN to learn the linear term and a dense fully-connected nonlinear NN to learn the nonlinear term. This contrasts with the standard neural ODE which involves training a single NN for the RHS. We apply this setup to the viscous Burgers equation, which exhibits shocked behavior, and show stabilized neural ODEs provide better short-time tracking, prediction of the energy spectrum, and robustness to noisy initial conditions than standard neural ODEs. We also apply this method to chaotic trajectories of the Kuramoto-Sivashinsky equation. In this case, stabilized neural ODEs keep long-time trajectories on the attractor, and are highly robust to noisy initial conditions, while standard neural ODEs fail at achieving either of these results. We conclude by demonstrating how stabilizing neural ODEs provide a natural extension for use in reduced-order modeling by projecting the dynamics onto the eigenvectors of the learned linear term.

Multi-parameter full waveform inversion using only the streamer data based on the acoustic-elastic coupled wave equation

The ocean seismic pressure data observed by hydrophones contain the elastic information of the subsurface medium, although few studies of full waveform inversion (FWI) regard the pressure data as generated from elastic media. Based on the acoustic-elastic coupled equation, which can directly obtain the elastic pressure component, we propose an acoustic-elastic FWI (AEFWI) method to use elastic pressure data. First, we illustrated the similarities and differences in wave propagation in acoustic and elastic media using ocean-bottom models. Furthermore, we compared the effect of pressure data with different degrees of elastic effects on acoustic FWI (AFWI) and AEFWI. It was found that the S-wave velocity at the seabed interface had a significant effect on the AFWI. When the seabed is soft, the results of AFWI are acceptable, whereas when the seabed is hard, the results of AFWI are nearly wrong, and the presence of elastic effects has to be considered in the inversion at this time. Contrastingly, the proposed method can obtain more accurate P- and S-wave velocities using only pressure data. Finally, the proposed method was applied to a real streamer dataset of the East China Sea, and high wavenumber P- and S-wave velocities were obtained. The RTM images illustrated the accuracy of the inversion results.

Single-Mode Solutions for Convection and Double-Diffusive Convection in Porous Media

This work employs single-mode equations to study convection and double-diffusive convection in a porous medium where the Darcy law provides large-scale damping. We first consider thermal convection with salinity as a passive scalar. The single-mode solutions resembling steady convection rolls reproduce the qualitative behavior of root-mean-square and mean temperature profiles of time-dependent states at high Rayleigh numbers from direct numerical simulations (DNS). We also show that the single-mode solutions are consistent with the heat-exchanger model that describes well the mean temperature gradient in the interior. The Nusselt number predicted from the single-mode solutions exhibits a scaling law with Rayleigh number close to that followed by exact 2D steady convection rolls, although large aspect ratio DNS results indicate a faster increase. However, the single-mode solutions at a high wavenumber predict Nusselt numbers close to the DNS results in narrow domains. We also employ the single-mode equations to analyze the influence of active salinity, introducing a salinity contribution to the buoyancy, but with a smaller diffusivity than the temperature. The single-mode solutions are able to capture the stabilizing effect of an imposed salinity gradient and describe the standing and traveling wave behaviors observed in DNS. The Sherwood numbers obtained from single-mode solutions show a scaling law with the Lewis number that is close to the DNS computations with passive or active salinity. This work demonstrates that single-mode solutions can be successfully applied to this system whenever periodic or no-flux boundary conditions apply in the horizontal.

Direct Numerical Simulation of Acoustic Turbulence: Zakharov–Sagdeev Spectrum

We present the results of direct numerical simulation of three-dimensional acoustic turbulence in medium with weak positive dispersion. It is shown that at the beginning of the long-wavelength region in the turbulence energy distribution in the k-space, there are formed jets in the form of narrow cones. At higher wavenumbers, the cones broaden, and the distribution accordingly tends to isotropic. In this region of wavenumbers, the angle-averaged turbulence spectrum acquires a power-law character, E(k) propto {{k}^{{ - alpha }}}, with the exponent close to 3/2, which corresponds to the Zakharov–Sagdeev weak acoustic turbulence spectrum.

Interaction of Serum Albumin and Fatty Acid Molecules with Graphenes of Shungite Carbon Nanoparticles in Aqueous Dispersion Assessed by Raman Spectroscopic Analysis of Water in the High Wavenumber Region

Interaction of Serum Albumin and Fatty Acid Molecules with Graphenes of Shungite Carbon Nanoparticles in Aqueous Dispersion Assessed by Raman Spectroscopic Analysis of Water in the High Wavenumber Region

On the role of spectral properties of viscous flux discretization for flow simulations on marginally resolved grids

In this note, the importance of spectral properties of viscous flux discretization in solving compressible Navier–Stokes equations for turbulent flow simulations is discussed. We studied six different methods, divided into two different classes, with poor and better representation of spectral properties at high wavenumbers. Both theoretical and numerical results have revealed that the method with better properties at high wavenumbers, denoted as α-damping type discretization, produced superior solutions compared to the other class of methods. The proposed compact α-damping method converged towards the direct numerical simulation (DNS) solution at lower grid resolution compared with the other class of methods and is, therefore, a better candidate for high fidelity large-eddy simulations (LES) and DNS studies.

A systematic study of a droplet breakup process in decaying homogeneous isotropic turbulence using a mesoscopic simulation approach

ABSTRACT The breakup of a spherical droplet in a decaying homogeneous isotropic turbulence is studied by solving the Cahn–Hilliard–Navier–Stokes equations. This flow provides a great opportunity to study the interactions of turbulent kinetic energy and interfacial free energy and their effects on the breakup dynamics. Three distinct stages of droplet evolution, namely, the deformation stage, the breakup stage, and the restoration stage, are identified and then analysed systematically from several perspectives: a geometric perspective, a dynamic perspective, a global energetic perspective, and a multiscale energy transfer perspective. It is found that the ending time of the breakup stage can be estimated by the Hinze criterion. The kinetic energy of the two-phase flow during the breakup stage is found to have a power-law decay with an exponent , compared to for the single-phase flow, mainly due to the enhanced viscous dissipation generated by the daughter droplets. Energy spectra of the two-phase flow show power-law decay, with a slope between and , at high wave numbers, both in the Fourier spectral space and in the spherical harmonics space.

Staircase solutions and stability in vertically confined salt-finger convection

Bifurcation analysis of confined salt-finger convection using single-mode equations obtained from a severely truncated Fourier expansion in the horizontal is performed. Strongly nonlinear staircase-like solutions having, respectively, one (S1), two (S2) and three (S3) regions of mixed salinity in the vertical direction are computed using numerical continuation, and their stability properties are determined. Near onset, the one-layer S1 solution is stable and corresponds to maximum salinity transport among the three solutions. The S2 and S3 solutions are unstable but exert an influence on the statistics observed in direct numerical simulations (DNS) in larger two-dimensional (2-D) domains. Secondary bifurcations of S1 lead either to tilted-finger (TF1) or to travelling wave (TW1) solutions, both accompanied by the spontaneous generation of large-scale shear, a process favoured for lower density ratios and Prandtl numbers ($Pr$). These states at low$Pr$are associated, respectively, with two-layer and three-layer staircase-like salinity profiles in the mean. States breaking reflection symmetry in the midplane are also computed. In two dimensions and for low$Pr$, the DNS results favour direction-reversing tilted fingers resembling the pulsating wave state observed in other systems. Two-layer and three-layer mean salinity profiles corresponding to reversing tilted fingers and TW1 are observed in 2-D DNS averaged over time. The single-mode solutions close to the high wavenumber onset are in an excellent agreement with 2-D DNS in small horizontal domains and compare well with 3-D DNS.

Manifestation of hydration of Na+ and Cl− ions in the IR spectra of NaCl aqueous solutions in the range of 2750–4000 cm−1

This work is aimed at the study at studying the influence of the interaction of solvate shells on the profiles of the IR spectra of sodium chloride solutions in the 2750–4000 cm−1 range. The IR spectra of distilled water and sodium chloride solutions were obtained with the limit (0.356 g per 100 g of water) and 50 % of the limit (0.178 g per 100 g of water) concentrations at a temperature of 21˚. Theoretical methods based on the use of the DFT approach with the XLYP exchange–correlation potential are used to calculate the profiles of the IR spectra of clusters containing 9 water molecules per one NaCl molecule at the limit concentrations of the solution. In the case when the cluster contained a NaCl molecule, the spectra were calculated for interacting and non-interacting solvate shells in which the number of H2O molecules varied from 3 to 6. The expansion of the experimental band profile on a basis containing the profiles of the theoretical bands made it possible to study the features of NaCl hydration with a change in the concentration of solutions. It was found that the IR spectrum band is formed mainly by interacting Na+ and Cl- solvation shells, each containing 4 H2O molecules, while the ninth H2O molecule provides the bond between the solvated ions. As the salt concentration increases, the contribution of the solvation shells to the band profile increases too. The agreement reached in the positions and profiles of experimental and theoretical water bands at different solution concentrations substantiates the adequacy of the theoretical description of NaCl hydration. Theoretical studies explained the effect of a decrease in the band width, an increase in the peak intensity, and a shift of its maximum toward higher wavenumbers with increasing solution concentration.

DNS analysis of turbulence modulation by lean premixed prevaporized spray flames in a model combustor

Turbulence modulation by lean premixed prevaporized (LPP) spray flames, which involve droplet motion, evaporation and gaseous reaction, is complicated and essential to organizing clean and efficient combustion. Direct numerical simulations of LPP combustion in a model swirling combustor under high pressure of 20 bar are performed. The gaseous flow is solved in the low-Mach-number limit, and the droplets are tracked as two-way coupled Lagrangian particles. The corrected infinite thermal conductivity model is adopted to describe droplet evaporation, and a reduced two-step kerosene/air chemistry mechanism is used to present combustion. Four cases, i.e., a non-reacting gaseous flow, a non-reacting spray flow and two reacting spray flows with different droplet sizes, are conducted to cover key features of LPP flame on turbulence modulation. The results show that the spray combustion significantly depresses the mean axial velocity on the centerline in the upstream, indicating an enhancement of the inner recirculation zone. The influence of droplets on the mean and fluctuating velocities is generally negligible except on the azimuthal modulation, while combustion can increase the velocities, which is more evident in downstream due to the pressure effect. In reacting cases, the turbulent kinetic energy (TKE) spectra in the shear layers reduce at high wavenumbers, reflecting the combustion-induced dissipation at small scales (below the laminar flame thickness scale). Besides, droplet evaporation can introduce energy at small scales while this modulation is balanced by combustion. Moreover, TKE budget analysis indicates that spray combustion mainly depresses the TKE and redistributes mean shear along the radial direction. Heat release increases the local fluid viscosity, depresses local turbulent transport, and increases viscous dissipation. Finally, the vortex stretching analysis shows that LPP combustion enhances the alignment with the intermediate strain rate component.

Fourier Transform Infrared Spectroscopy in the Study of Discrimination of Lobular Breast Cancers.

The early diagnosis of breast cancer plays an important role in reducing mortality and optimizing the prognosis of the disease. The existing visual and histopathological methods do not give any information at a molecular level. Fourier transform infrared spectroscopy does not require any preparation, such as fixation and histological stains. The collected infrared spectral "biomarker bands" give information at a molecular level and could be used for biomarker screening, in order to minimize the false-positive or false-negative results. For this prospective study, nine biopsies of lobular carcinoma (7 in situ and 2 invasive) and the adjacent healthy region of the biopsies were used. Each infrared spectrum consisted of 120 scans/spectrum (120 co-added spectra) at a spectral resolution of 4 cm -1 . The infrared spectral analysis revealed three important "diagnostic spectral regions" between 3,300-2,850 cm -1 , 1,700-1,500 cm -1 , and 850-800 cm -1 , which are related to membrane, collagen, and DNA configuration damage, respectively. The shift of the absorption band at 1,161 cm -1 at higher wave numbers up to 1,172 cm -1 is assigned to vC-O-C bonds due to membrane, protein, and DNA glycosylation. The "biomarker bands" at 1,172 cm -1 can be used as "diagnostic marker bands" for cancer progression. The shift of the absorbance band at 825 cm -1 of the native configuration of B-DNA to lower wavenumbers at 810 cm -1 Z-DNA in grade III, suggests the irreversible stage of the disease. The detection and possibility to differentiate the DNA structures may allow detection of carcinogenesis at the early stage of the disease, and development of new anticancer therapies.

Receiver circuit improvement of dual frequency-comb ka-band Doppler backscattering system in the large helical device (LHD).

Doppler-backscattering (DBS) has been used in several fusion plasma devices because it can measure the perpendicular velocity of electron density perturbation v⊥, the radial electric field Er, and the perpendicular wavenumber spectrum S(k⊥) with high wavenumber and spatial resolution. In particular, recently constructed frequency comb DBS systems enable observation of turbulent phenomena at multiple observation points in the radial direction. A dual-comb microwave DBS system has been developed for the large helical device plasma measurement. Since it is desirable to control the gain of each frequency-comb separately, a frequency-comb DBS system was developed with a function to adjust the gain of the scattered signal intensity of each channel separately. A correction processing method was also developed to correct the amplitude ratio and the phase difference between the in-phase and quadrature-phase signals of the scattered signals. As a result, the error in Doppler-shift estimation required to observe vertical velocity and the radial electric field was reduced, which enables more precise measurements.

Phototactic isotropic scattering bioconvection with oblique irradiation

The phenomenon of collective movements of microorganisms is referred to as “bioconvection.” Negative phototaxis refers to motions directed away from the source of illumination, and positive phototaxis refers to motions directed in that direction. In this study, numerical analysis is performed on both the steady-state and linear stability solutions of the isotropic scattering suspension with oblique collimated irradiation. The bottom boundary is taken to be rigid and the top is either stress-free or rigid. The governing equations are solved using a fourth-order Newton–Raphson–Kantorovich iteration-based finite-difference accurate method. Through variation in the angle of incidence, we found two different types of nature for lower and higher scattering albedo in the basic state concentration profile. In the case of a rigid (or stress-free) upper boundary, the bioconvection solutions are generally oscillatory (or stationary) and more stable (or unstable). The scattering model coincides with the up-swimming model at higher wavenumbers.

Gyro-averaging operators with magnetic field inhomogeneity

We derive expressions for the gyro-averaging operator that is applicable to electrostatic fluctuations in a spatially inhomogeneous magnetic field. Both low and high wavenumber limits are considered. The gyro-averaging operator for the former case is represented by sums of Bessel functions with different orders. A simplified expression is provided as a Padé approximant in the low wavenumber limit. This form could be used in practical computations based on the gyrofluid formulation. In the high wavenumber limit, we find that the operator naturally involves fractional derivatives whose physical interpretations are yet to be explored. Discussions are made of a potential impact of this asymptotic expression in the high wavenumber limit.

Effects of equatorially-confined shear flow on MRG and Rossby waves

Linear modal stability analysis of a mean zonal shear flow is carried out in the framework of rotating shallow water equations (RSWE), both under the β-plane approximation and in the full spherical coordinate system. Two base flows – equatorial easterly (EE) and westerly (EW) – with Gaussian profiles highly confined to small latitudes are analysed. At low Froude number, mixed Rossby-gravity (MRG) and Rossby waves are found to be particularly affected by shear, with prominent changes at higher wavenumbers. These waves become practically non-dispersive at large wavenumbers in EE. The perturbations are found to be more confined equatorially in EE than in EW with the degree of confinement being more pronounced in the β-plane system compared to the full spherical system. At high Froude number, the phase speeds are significantly larger in the β-plane system for all families of waves. Under the β-plane approximation, exponentially unstable modes can be excited, having negative (positive) phase speed in EE (EW). Strikingly, this flow is always neutrally stable with the full spherical system. This speaks for the importance of studying the whole spherical system even for equatorially confined shear.

Improved MAX-MIN method to estimate total magnetization direction using Wiener filtering

Knowledge of the total magnetization direction is useful for forward modeling and reduction-to-the-pole (RTP) of magnetic anomalies. However, remanent magnetization deviates the total magnetization direction from the induced magnetization direction; therefore, it is essential to determine the correct direction of total magnetization. Theoretically, the MAX-MIN method, which searches for the position of the maximum value of the function that comprises the minimum values of the RTP field with different directions, can yield the correct direction of total magnetization. However, such estimations of direction usually indicate large errors in comparison with the results of crosscorrelation methods, which calculate the correlation coefficient between the RTP field and the magnetic magnitude transforms. Our analysis reveals that noise is the primary cause of the inaccuracy in estimation results. We have improved the MAX-MIN method using Wiener filtering based on the principle of least-mean-squares deviation. The k-means clustering algorithm clusters points that are as closely connected as possible, while ensuring that the distances between clusters are as large as possible. Therefore, the k-means clustering algorithm is used to divide the radial logarithmic power spectrum into the effective signal with low wavenumbers and the noisy signal with high wavenumbers. Then, the Wiener filtering RTP operator is constructed using the slope and intercept of the fitted straight line in the corresponding wavenumber bands. The improved MAX-MIN method is tested using magnetic anomalies of spherical and combined cuboid models with different levels of added Gaussian noise and different total magnetization directions. The improved MAX-MIN method is applied to the magnetic anomaly in the Yeshan region (eastern China) and the Taihe region (southwestern China). Results indicate that the improved MAX-MIN method based on the principle of least-mean-squares deviation could obtain reliable estimation of direction from noisy magnetic anomaly data.

Evaluation of Strained Group IV Semiconductor Devices by Oil-Immersion Raman Spectroscopy

1. Background and purpose Strain techniques are one of the principal technology boosters for the realization of high-performance logic devices composed of group IV semiconductors such as Si, Ge and their alloy. Recently, it is gradually difficult to measure strain states as miniaturization proceeds to the nanometer scale. Raman spectroscopy is one of the most powerful techniques for phonon measurements and can perform strain evaluation with high spatial resolution nondestructively [1]. However, conventional Raman spectroscopy is limited in strain information based on the Raman polarization selection rules [1].In this paper, we introduce oil-immersion Raman spectroscopy with the high-numerical-aperture (high-NA) lens to realize precise evaluation of strain states (for example, anisotropic strain) in group IV semiconductor devices. 2. Oil-immersion Raman spectroscopy In conventional Raman spectroscopy, it is impossible to excite transverse optical (TO) phonon mode due to Raman polarization selection rules under the backscattering geometry from the (001) group IV semiconductor surface. In other words, a uniaxial or isotropic biaxial stress measurements in group IV semiconductors can only be performed by exciting only the longitudinal optical (LO) phonon mode under a conventional (001) backscattering configuration.To realize anisotropic stress evaluation assuming the channel region of the group-IV semiconductor MOSFET, we used a high-NA immersion lens for the selective excitation of both LO and TO phonon modes. The high-NA and refractive index n of the oil were approximately 1.4 and 1.5, respectively. Using a high-NA immersion lens, a z-polarized light component can be effectively obtained owing to the aperture angle. Therefore, TO phonons can be excited on the basis of Raman selection rules for (001)-oriented group IV semiconductors [2, 3]. 3. Results and discussion As an example of oil-immersion Raman measurements results, we evaluated the strain states of extremely-thin-body Ge-on-insulator (ETB GOI) MOSFET channels fabricated by Ge condensation [4, 5] by oil-immersion Raman spectra. We observed that the Raman peak shifted toward a higher wavenumber, indicating that high compressive strain in the GOI channels. In addition, a clear splitting of LO and TO phonon modes was confirmed, implying the anisotropic biaxial strain states induced in the ETB GOI channel.Figure 1 shows the channel width (Wch) dependence of the anisotropic biaxial stress for ETB GOI MOSFET (channel thickness: 10.6 nm) obtained by the oil-immersion Raman spectroscopy. As shown in Fig. 1, the stress relaxation along the GOI channels was observed as the GOI channel width gets narrower. In other words, the uniaxial stress is applied into channels by narrow GOI channel patterning. These behaviors are in good agreement with the previous reports such as strained-SOI [6] and SiGe nano patterns [3][7].In conclusion, oil-immersion Raman spectroscopy is one of the most powerful strain measurements in Group IV semiconductor device structures. Acknowledgements This work was supported by JSPS KAKENHI Grant Number 22H00208, Japan. A part of this work was conducted at Takeda Sentanchi Supercleanroom, The University of Tokyo, supported by "Nanotechnology Platform Program" of MEXT, Japan, Grant Number JPMXP09F-20-UT-0007.